DESCRIPTION: There is public concern about the health risks of exposure to the electric and magnetic fields generated by power distribution systems. The objective of this program is to provide human data to test two hypotheses about how the epidemiological link between exposure to magnetic fields and increased risk of cancer might come about. The specific aims of the work are to: 1) replicate a previous study indicating that magnetic field exposure at 20 uT suppresses nocturnal melatonin (MLT) in men with low basal level of MLT, and to further define effective field exposure characteristics; 2) determine whether similar effects happen in women; 3) test the hypothesis that exposure- related suppression of MLT is associated with alterations in relevant hormones; and 4) test the hypothesis that exposure-related suppression of MLT is associated with changes in specific immune system components.Three double-blind studies will be performed. Each study will take into account individual differences in basal MLT levels (0200 peak) prior to exposure as well as sensitivity to bright light, a known suppressor of MLT. The first study will replicate their previous human exposure study, and determine the most effective magnetic field type (continuous rotating, intermittent with minimal harmonic content, or intermittent with high harmonic content.) Exposure will be from 2300 to 0700.Blood samples for MLT analysis will be obtained every hour. Samples of testosterone and interleukin 2 will be obtained at 2300, 0300, and 0700. The second study will use similar procedures, except that one group of men and two groups of healthy young women will be included. One group of women will be tested in the luteal and the other in the follicular phase of the menstrual cycle. Half of each group will be exposed to the most effective field from Study 1, and half will be sham exposed. Outcome measures will include MLT, estradiol, prolactin, testosterone, and cortisol. Data from this study will be used to test the hypothesis that magnetic field exposure alters MLT which in turn alters estradiol and prolactin.A similar design will be used for the fourth study except that immune system components (activated T-cell counts and function; B- cell function, natural killer cell function, selected cytokines) will be the outcome measures. Information of the type to be obtained in the proposed research is needed to aid in risk assessment, and, if no meaningful effects are found, to alleviate unwarranted public concern.